1. Field of the Invention
The present invention relates to fuel cell systems and operation methods therefor. More specifically, the present invention relates to fuel cell systems and operation methods therefor where power generation in the fuel cell is continued even after receiving an operation stop command, in order to charge a secondary battery if the secondary battery has not been charged to a predetermined extent.
2. Description of the Related Art
Fuel cell systems mounted on transportation equipment and electronic apparatuses make use of a secondary battery for driving system components in order to start power generation in the fuel cells. In these fuel cell systems, it is a common practice to continue power generating operation in the fuel cells even after receiving an operation stop command if the secondary battery has not been charged to a predetermined threshold. By charging the secondary batteries in this way, these systems can make a reliable transfer to normal operation where uninterrupted normal power generation takes place, when the system is turned on next time.
An example of a conventional device of this kind is disclosed in JP-A 2004-227832 (Patent Document 1), for example. Specifically, the document discloses a technique whereby power generation by the fuel cells is forcibly terminated even during a battery charging operation after an operation stop command is received. Stopping the power generation in the fuel cells, i.e. stopping the charging of the secondary battery, increases convenience of the system operator since the operator no longer has to wait until the charging is complete after issuing the operation stop command.
However, since it is possible to abort charging after the operation stop command is issued, the technique according to Patent Document 1 poses a risk that the amount of charge stored in the secondary battery will be depleted in the next cycle of operation, before the fuel cell's output covers the system's power consumption. This means that the fuel cells become unable to sustain power generation, and the fuel cell system ceases its operation before entering into normal operation.